在驱动器上运行文件系统观察器时，无法弹出安全取出的 U 盘

我需要在我的 USB 驱动器上创建一个记录文件活动。

到目前为止我能做什么：

它使用 ManagementEventWatcher 检测 USB 存储器的插入和提取(检测内存被移除后的提取)：

using System.Management;
var insertQuery = new WqlEventQuery("SELECT * FROM Win32_VolumeChangeEvent WHERE EventType = 2");
var insertWatcher = new ManagementEventWatcher(insertQuery);
insertWatcher.EventArrived += DeviceInsertedEvent;
insertWatcher.Start();

使用FileSystemWatcher我可以记录所有操作，例如创建，修改，删除和重命名的文件：

FileSystemWatcher m_Watcher = new FileSystemWatcher();
m_Watcher.Path = e.PathDevice + "\";
string strFilter = "*.*";
m_Watcher.Filter = strFilter;
m_Watcher.NotifyFilter = 
NotifyFilters.Attributes |
NotifyFilters.FileName;
m_Watcher.IncludeSubdirectories = true;
m_Watcher.Created += new FileSystemEventHandler(OnCreated);
m_Watcher.EnableRaisingEvents = true;

问题：

当 FileSystemWatcher 正在查看该单元时，如果我尝试安全地弹出该单元，它会告诉我我不能，因为我的应用程序进程正在使用它。此变量设置为 true 时EnableRaisingEvents = true;使事件能够侦听内存中的更改，并且是不允许我安全删除内存的变量，我做了一个测试并启动了应用程序，我将其设置为 falseEnableRaisingEvents = false;我可以安全地删除内存。

可能的解决方案：

如何在操作系统删除设备之前检测到设备的删除？这样，我可以停止在设备上使用文件系统观察器并安全地删除USB设备。

经过几天的寻找种植问题的答案，我找到了解决方案。

这篇文章对解决问题和这个问题非常有帮助。

如果我们使用服务或 Windows 表单应用程序，解决方案会发生变化。我的答案是基于服务。

服务有一个控制处理程序，用于接收来自 Windows 的所有消息。这些可能包括停止或暂停服务的代码，或者如本例所示的设备事件。我们需要注册自己的服务处理程序，以便可以捕获设备事件。这将禁用所有回调，例如 OnStop，但 OnStart 除外，它是在我们告诉 Windows 使用我们的处理程序之前调用的。

用于此目的的 Windows API 函数是 RegisterServiceCtrlHandlerEx，它接受服务名称和在收到消息时要调用的回调函数。我们将在服务中的 OnStart 函数中调用它。

服务控制处理程序的签名如下所示：

public delegate int ServiceControlHandlerEx(int control，int eventType， IntPtr eventData， IntPtr context);

public partial class Service1 : ServiceBase{
private FileSystemWatcher fileSystemWatcher;
private IntPtr deviceNotifyHandle;
private IntPtr deviceEventHandle;
private IntPtr directoryHandle;
private Win32.ServiceControlHandlerEx myCallback;
public Service1()
{
InitializeComponent();
}
protected override void OnStart(string[] args)
{
base.OnStart(args);
//
RegisterDeviceNotification();
fileSystemWatcher = new FileSystemWatcher();
fileSystemWatcher.Created += new System.IO.FileSystemEventHandler(fileSystemWatcher_Created);
fileSystemWatcher.Deleted += new System.IO.FileSystemEventHandler(fileSystemWatcher_Deleted);
fileSystemWatcher.Changed += new System.IO.FileSystemEventHandler(fileSystemWatcher_Changed);
fileSystemWatcher.Renamed += new System.IO.RenamedEventHandler(fileSystemWatcher_Renamed);
}
}

注册设备通知

在 OnStart 方法中，除了注册控件处理程序外，我们还将使用Win32API 函数 RegisterDeviceNotification 注册设备通知。我们给它服务的句柄，一个指向DEV_BROADCAST_DEVICEINTERFACE结构的指针(告诉函数注册一类设备)和一些标志，其中包括DEVICE_NOTIFY_SERVICE_HANDLE，例如，它指定调用方是服务而不是窗口。它返回一个句柄，我们必须保留该句柄，以便在不再需要设备消息时取消注册(例如，我们可以在SERVICE_CONTROL_STOP事件中执行此操作)。

使用此函数，我们可以捕获DBT_DEVICEARRIVAL和DBT_DEVICEREMOVECOMPLETE事件类型。我们通过服务控制处理程序的 eventType 参数获取它们。在那里，我们可以处理SERVICE_CONTROL_DEVICEEVENT并做任何我们喜欢的事情。

public void RegisterDeviceNotification()
{
InitArrayDevNotifyHandle();
myCallback = new Win32.ServiceControlHandlerEx(ControlHandler);
Win32.RegisterServiceCtrlHandlerEx(service.ServiceName, myCallback, IntPtr.Zero);
if (service.GetServiceHandle() == IntPtr.Zero)
{
// TODO handle error
}
Win32.DEV_BROADCAST_DEVICEINTERFACE deviceInterface = new Win32.DEV_BROADCAST_DEVICEINTERFACE();
int size = Marshal.SizeOf(deviceInterface);
deviceInterface.dbcc_size = size;
deviceInterface.dbcc_devicetype = Win32.DBT_DEVTYP_DEVICEINTERFACE;
IntPtr buffer = default(IntPtr);
buffer = Marshal.AllocHGlobal(size);
Marshal.StructureToPtr(deviceInterface, buffer, true);
deviceEventHandle = Win32.RegisterDeviceNotification(service.GetServiceHandle(), buffer, Win32.DEVICE_NOTIFY_SERVICE_HANDLE | Win32.DEVICE_NOTIFY_ALL_INTERFACE_CLASSES);
if (deviceEventHandle == IntPtr.Zero)
{
// TODO handle error
}
}

DBT_DEVICEQUERYREMOVE - 解决方案

这是回答问题的主要内容我需要通知应用程序对设备的硬件配置进行更改。具体来说，在 SO 之前更换 USB 存储器将移除内存。多亏了@ZdeněkJelínek我才能找到该事件，DBT_DEVICEQUERYREMOVE请求删除设备或介质的权限。此事件在即将删除设备之前举行。

解决方案是创建设备本身的句柄，在DEV_BROADCAST_HANDLE结构中使用它，并将其注册到我们的服务控制处理程序。为了完成所有这些，需要做几件事：

查找设备的驱动器号。我能够使用ManagementEventWatcher类，它允许我订阅设备插入事件，它为我提供有关插入设备的信息。所有这些都是用完成的，以便使用CreateFileHandle函数获取设备句柄。只有在那之后，我们才能获取DBT_DEVICEQUERYREMOVE事件，禁用FileSystemWatcher，并允许自由删除USB。

private int ControlHandler(int control, int eventType, IntPtr eventData, IntPtr context)
{
if (control == Win32.SERVICE_CONTROL_STOP || control == Win32.SERVICE_CONTROL_SHUTDOWN)
{
UnregisterHandles();
Win32.UnregisterDeviceNotification(deviceEventHandle);
base.Stop();
}
else if (control == Win32.SERVICE_CONTROL_DEVICEEVENT)
{
string c;
switch (eventType)
{
case Win32.DBT_DEVICEARRIVAL:
//This is an example ... I do not use the DBT_DEVICEARRIVAL event, but it can be used. Instead use the ManagementEventWatcher class to detect when a device arrives and driveLetter.
RegisterForHandle(driveLetter);
fileSystemWatcher.Path = driveLetter + ":\";
fileSystemWatcher.EnableRaisingEvents = true;
break;
case Win32.DBT_DEVICEQUERYREMOVE:
Win32.DEV_BROADCAST_HDR hdrR;
Win32.DEV_BROADCAST_HANDLE dbhdl;
hdrR = (Win32.DEV_BROADCAST_HDR)
Marshal.PtrToStructure(eventData, typeof(Win32.DEV_BROADCAST_HDR));
if (hdrR.dbcc_devicetype == Win32.DBT_DEVTYP_HANDLE)
{
dbhdl = (Win32.DEV_BROADCAST_HANDLE)
Marshal.PtrToStructure(eventData, typeof(Win32.DEV_BROADCAST_HANDLE));
UnregisterHandles();
fileSystemWatcher.EnableRaisingEvents = false;
fileSystemWatcher = null;
}
break;
}
}
return 0;
}

private void UnregisterHandles()
{
if (directoryHandle != IntPtr.Zero)
{
Win32.CloseHandle(directoryHandle);
directoryHandle = IntPtr.Zero;
}
if (deviceNotifyHandle != IntPtr.Zero)
{
Win32.UnregisterDeviceNotification(deviceNotifyHandle);
deviceNotifyHandle = IntPtr.Zero;
}
}
private void RegisterForHandle(char c)
{
Win32.DEV_BROADCAST_HANDLE deviceHandle = new Win32.DEV_BROADCAST_HANDLE();
int size = Marshal.SizeOf(deviceHandle);
deviceHandle.dbch_size = size;
deviceHandle.dbch_devicetype = Win32.DBT_DEVTYP_HANDLE;
directoryHandle = CreateFileHandle(c + ":\");
deviceHandle.dbch_handle = directoryHandle;
IntPtr buffer = Marshal.AllocHGlobal(size);
Marshal.StructureToPtr(deviceHandle, buffer, true);
deviceNotifyHandle = Win32.RegisterDeviceNotification(this.ServiceHandle, buffer, Win32.DEVICE_NOTIFY_SERVICE_HANDLE);
if (deviceNotifyHandle == IntPtr.Zero)
{
// TODO handle error
}
}
public static IntPtr CreateFileHandle(string driveLetter)
{
// open the existing file for reading          
IntPtr handle = Win32.CreateFile(
driveLetter,
Win32.GENERIC_READ,
Win32.FILE_SHARE_READ | Win32.FILE_SHARE_WRITE,
0,
Win32.OPEN_EXISTING,
Win32.FILE_FLAG_BACKUP_SEMANTICS | Win32.FILE_ATTRIBUTE_NORMAL,
0);
if (handle == Win32.INVALID_HANDLE_VALUE)
{
return IntPtr.Zero;
}
else
{
return handle;
}
}

public class Win32
{
public const int DEVICE_NOTIFY_SERVICE_HANDLE = 1;
public const int DEVICE_NOTIFY_ALL_INTERFACE_CLASSES = 4;
public const int SERVICE_CONTROL_STOP = 1;
public const int SERVICE_CONTROL_DEVICEEVENT = 11;
public const int SERVICE_CONTROL_SHUTDOWN = 5;
public const uint GENERIC_READ = 0x80000000;
public const uint OPEN_EXISTING = 3;
public const uint FILE_SHARE_READ = 1;
public const uint FILE_SHARE_WRITE = 2;
public const uint FILE_SHARE_DELETE = 4;
public const uint FILE_ATTRIBUTE_NORMAL = 128;
public const uint FILE_FLAG_BACKUP_SEMANTICS = 0x02000000;
public static readonly IntPtr INVALID_HANDLE_VALUE = new IntPtr(-1);
public const int DBT_DEVTYP_DEVICEINTERFACE = 5;
public const int DBT_DEVTYP_HANDLE = 6;
public const int DBT_DEVICEARRIVAL = 0x8000;
public const int DBT_DEVICEQUERYREMOVE = 0x8001;
public const int DBT_DEVICEREMOVECOMPLETE = 0x8004;
public const int WM_DEVICECHANGE = 0x219;
public delegate int ServiceControlHandlerEx(int control, int eventType, IntPtr eventData, IntPtr context);
[DllImport("advapi32.dll", SetLastError = true)]
public static extern IntPtr RegisterServiceCtrlHandlerEx(string lpServiceName, ServiceControlHandlerEx cbex, IntPtr context);
[DllImport("kernel32.dll", SetLastError = true)]
[return: MarshalAs(UnmanagedType.Bool)]
public static extern bool GetVolumePathNamesForVolumeNameW(
[MarshalAs(UnmanagedType.LPWStr)]
string lpszVolumeName,
[MarshalAs(UnmanagedType.LPWStr)]
string lpszVolumePathNames,
uint cchBuferLength,
ref UInt32 lpcchReturnLength);
[DllImport("kernel32.dll")]
public static extern bool GetVolumeNameForVolumeMountPoint(string
lpszVolumeMountPoint, [Out] StringBuilder lpszVolumeName,
uint cchBufferLength);
[DllImport("user32.dll", SetLastError = true)]
public static extern IntPtr RegisterDeviceNotification(IntPtr IntPtr, IntPtr NotificationFilter, Int32 Flags);
[DllImport("user32.dll", CharSet = CharSet.Auto)]
public static extern uint UnregisterDeviceNotification(IntPtr hHandle);
[DllImport("kernel32.dll", SetLastError = true)]
public static extern IntPtr CreateFile(
string FileName,                    // file name
uint DesiredAccess,                 // access mode
uint ShareMode,                     // share mode
uint SecurityAttributes,            // Security Attributes
uint CreationDisposition,           // how to create
uint FlagsAndAttributes,            // file attributes
int hTemplateFile                   // handle to template file
);
[DllImport("kernel32.dll", SetLastError = true)]
public static extern bool CloseHandle(IntPtr hObject);
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
public struct DEV_BROADCAST_DEVICEINTERFACE
{
public int dbcc_size;
public int dbcc_devicetype;
public int dbcc_reserved;
[MarshalAs(UnmanagedType.ByValArray, ArraySubType = UnmanagedType.U1, SizeConst = 16)]
public byte[] dbcc_classguid;
[MarshalAs(UnmanagedType.ByValArray, SizeConst = 128)]
public char[] dbcc_name;
}
[StructLayout(LayoutKind.Sequential)]
public struct DEV_BROADCAST_HDR
{
public int dbcc_size;
public int dbcc_devicetype;
public int dbcc_reserved;
}
[StructLayout(LayoutKind.Sequential)]
public struct DEV_BROADCAST_HANDLE
{
public int dbch_size;
public int dbch_devicetype;
public int dbch_reserved;
public IntPtr dbch_handle;
public IntPtr dbch_hdevnotify;
public Guid dbch_eventguid;
public long dbch_nameoffset;
public byte dbch_data;
public byte dbch_data1;
}
}

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